Stroke, Alzheimer's disease, Parkinson's disease, demyelinating disease, spinal cord injury, etc. are diseases caused by nerve dysfunction due to nerve cell damage. Methods for treating nerve cells damaged by these diseases typically include drug therapy and surgical operation, but these treatments may also damage normal cells, which is problematic.
Accordingly, cell therapy products used to replace cells lost or damaged by disease with normal cells have recently been proposed. Stem cells have attracted much attention as one of the cell therapy products.
Studies suggesting that mesenchymal stem cells (MSCs) can differentiate into neural cells have been published since the early 2000's and have extended to in vivo studies as well as in vitro studies. In order to examine the signal transduction mechanisms and changes in gene expression during the differentiation of mesenchymal stem cells into neural cells, in vivo transplantation studies are ultimately required, but there are also disadvantages such as high costs and time and many obstacles (various signal transductions), and thus it is not easy to conduct such studies. Moreover, as the cell therapy products for regenerative medicine in the future, it is not clear whether undifferentiated MSCs or neural-committed MSCs are effective for in vivo transplantation. Accordingly, in order to solve these problems, it is necessary to establish an appropriate technology that can differentiate mesenchymal stem cells into neural cells in vitro. There are generally two neural cell differentiation methods; one is chemical differentiation and the other is growth factor or cytokine differentiation. Chemical differentiation uses antioxidants, such as β-mercaptoethanol (BME), butylated hydroxyanisole (BHA), butylated hydroxyl toluene (BHT), retinoic acid (RA), etc., and induces the expression of neuronal markers, such as neuron-specific enolase (NSE), neurofilament (NF), neuronal nuclei (NeuN), etc., together with more severe morphological changes than the growth factor or cytokine differentiation. However, it is known that more than 50% cells undergo apoptosis along with these changes within 24 hours from the induction, and it is also known that chemicals induce cellular stress, which causes physical contraction of cells, like neurons, resulting in no expression of neuronal markers. This phenomenon occurs similarly when harmful substances are treated with other types of primary cells or transformed cells, and when summarizing these results, the treatment with antioxidants does not induce transdifferentiation into neural cells but simply causes environmental stress.
The growth factor or cytokine differentiation is a method for differentiating stem cells into neural cells by treatment with epidermal growth factor (EGF), fibroblast growth factor (FGF), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), etc. and does not cause environmental stress or cell apoptosis. However, it takes more than 4 weeks to induce differentiation, which significantly increases the cost of differentiation. Nevertheless, the rate of differentiation into neurons is significantly low, and the expression of neuronal markers is different from that of mature neurons, which are also problematic.
Meanwhile, lipoic acid is a fatty acid containing sulfur atoms, represented by the following Formula 1, and is known as an alpha-lipoic acid. Moreover, it participates in energy metabolism that converts glucose into energy and is present in all eukaryotic cells. Furthermore, it is reported that lipoic acid essentially has antioxidation activity and thus also has anti-apoptotic activity. Accordingly, it is much used in serum-free culture of human cells, but is known to cause cell apoptosis at a concentration of 2 mM or higher and thus is used at concentrations as low as 25 to 100 μM.

Accordingly, the present inventors have developed a new chemical neuronal differentiation method, which uses lipoic acid and albumin that reduces the toxicity of lipoic acid at high concentrations of lipoic acid and allows lipoic acid to be slowly released under culture conditions, and revealed that forskolin exhibits an additional synergistic effect on the neuronal differentiation, thereby completing the present invention.